In my sternum, i have what seems to be something exerting pressure on the bottom. it leaves an annoying feeling that causes me discomfort. what is it?

An Alien: You may have a deformity in your sternum (example: pectus excavatum) that can sometimes be irritating. If you have discomfort below the "xiphoid" (lower tip of the sternum), it may be from trauma, or it may be underneath which could be your stomach or esophagus. Get a doctor to examine you.

Chostochondritis?: Irritation or inflammation of the cartilage connecting the sternum and ribs is called chostochondritis. It can be traumatic (most common) or idiopathic (no known cause). The xiphoid process is a bone hooked to the bottom of your sternum. It could also be irritated in that area.